Effect of temperature and atmosphere on oxidation kinetics and oxide scale characteristics of Ni-containing steel during heat treatment
This study systematically investigated the effect of heat treatment temperature and atmosphere on the oxidation ki-netics and oxide scale characteristics of a(0.04%～0.07%)C-(7%～8%)Ni steel.The results show that within the temperature range of 800～950℃,reducing the partial pressure of oxygen in the gas phase significantly suppresses oxidation weight gain.Concurrently,the oxidation kinetics curve shifts from linear to parabolic,indicating that the rate-controlling step changes from chemical reaction to diffusion-controlled mass transfer.Due to the formation of a network-like structure in the inner oxidation layer,where Ni-rich metallic phases and Fe oxides interlock with each other,the descalability of oxide scale on the steel sur-face is impaired.As the oxidation temperature increases,the thickness of the external oxide scale increases under all atmo-spheres tested.However,the evolution of the inner oxide layer varies:in air,its thickness consistently increases with tempera-ture,whereas in nitrogen atmosphere,it first increases and then decreases,becoming almost negligible at 950℃.This phenom-enon can be attributed to the growth of the external oxide scale at high temperatures,which reduces the oxygen concentration gradient at the gas/oxide scale interface and thus inhibits inner oxidation.
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